Peri-implant reactivity and osteoinductive potential of immobilized rhBMP-2 on titanium carriers.

Recombinant human BMP-2 (rhBMP-2) was immobilized non-covalently and covalently as a monolayer on plasma vapour deposited (PVD) porous commercially pure titanium surfaces in amounts of 5-8 µg cm(-2), providing a ca. 10-fold increase vs. previously reported values. Dissociation of the immobilized [125I]rhBMP-2 from the surface occurred in a two-phase exponential decay: a first rapid phase (ca. 15% of immobilized BMP-2) with a half-life of 1-2 days and a second slow sustained release phase (ca. 85% of immobilized BMP-2) with a half-life of 40-60 days. Dissociation rate constants of sustained release of k(-1)=1.3-1.9 x 10(-7)s(-1) were determined, allowing an estimation of the binding constants (K(A)) for the adsorbed rhBMP-2 monolayer, to be around 10(12) M(-1). The rhBMP-2-coated surfaces showed a high level of biological activity, as demonstrated by in vitro epifluorescence tests for alkaline phosphatase with MC3T3-E1 cells and in vivo experiments. In vivo osteoinductivity of rhBMP-2-coated implants was investigated in a gap-healing model in the trabecular bone of the distal femur condylus of sheep. Healing occurred without inflammation or capsule formation. The calculated concentration of released rhBMP-2 in the 1mm gap ranged from 20 to 98 nM--well above the half-maximal response concentration (K(0.5)) for inducing alkaline phosphatase in MC3T3-E1 cells. After 4, 9 and 12 weeks the bone density (BD) and bone-to-implant contact (BIC) of the explanted implants were assessed histomorphometrically. Implants with immobilized rhBMP-2 displayed a significant (2- to 4-fold) increase in BD and BIC values vs. negative controls after 4-9 weeks. Integration of implants by trabecular bone was achieved after 4 weeks, indicating a mean "gap-filling rate" of ∼250 µm week(-1). Integration of implants by cortical bone was observed after 9 weeks. Control implants without rhBMP-2 were not osseointegrated. This study demonstrates the feasibility of enhancing peri-implant osseointegration and gap bridging by immobilized rhBMP-2 on implant surfaces which may serve as a model for future clinical applications.

[Cement-in-cement hip revision with a long-stemmed femoral component]. / Zement-in-Zement-Hüftrevision mit einem zementierten langen Prothesenstiel.

Revision hip surgery often requires individualized techniques and implants. We report on a case of failed femoral revision in an extensively cemented femur with a concomitant proximal and dorsal femoral bone defect. We advocate the clinically effective revision procedure of antegrade drilling of the stable cement mantle and use of a cemented long-stemmed femoral component. This cement-in-cement revision technique is discussed along with the pertinent literature.

[Rotating platform spinout in LCS knee arthroplasty]. / Spinout der rotierenden Plattform bei der LCS-Knieendoprothese.

In knee arthroplasty, a lax flexion gap may cause flexion instability. Subsequently, the operated knee may subluxate or dislocate. We report on a case of recurrent subluxations with malrotation of the rotating platform (spinout) after primary LCS total knee arthroplasty. Potential causes for spinout, therapy procedures, and consequences for the primary surgical technique are discussed. In the LCS rotating platform knee arthroplasty, the flexion gap must not be laxer than the extension gap. In such an instance, we recommend a higher rotating platform and a more proximal distal transverse femoral osteotomy.

[Ultrasound in the early diagnosis of congenital dislocation of the patella]. / Sonographische Frühdiagnose der kongenitalen Patellaluxation.

INTRODUCTION: Congenital dislocation of the patella is defined as lateral dislocation of the patella present at birth, impossibility of closed reduction and diagnosis before the age of 10 years. We report about a rare case of a bilateral congenital dislocation of the patella. CASE REPORT: Physical examination of an eight-month- old boy showed bilateral knee flexion contractures associated with moderate genu varum. On both sides the patella could not be palpated easily. Radiographic diagnosis could not show the patella as the patella normally ossifies later. Ultrasound examination located the patella lateral to the lateral femoral condyle on both sides. Closed reduction was impossible. An open reduction with division of the lateral soft tissues, lateral release, and derotation of the quadriceps femoris and refining of the medial structures was performed. After cast removal the patellae were both located in the intercondylar grooves as confirmed by clinical and ultrasound examinations of both knees. Active and passive exercises were started. CONCLUSION: Failure of internal rotation of the myotome which contains the quadriceps femoris and the patella is the etiology of congenital dislocation of the patella. The quadriceps acts as flexor, exerting a valgus stress on the knee, causing external rotation of the tibia. Diagnosis is often delayed because of the lack of pathological findings on plain radiographs. Early diagnosis is enabled by ultrasonography. Surgical treatment is necessary and results are good, as long as there are no secondary changes.

[Unusual course of sacrococcygeal chordoma]. / Ungewöhnlicher Verlauf eines sacrococcygealen Chordoms.

Observation of a sacrococcygeal chordoma with exceptional long survival of now 17 years after incomplete surgery with following additional resection and adjuvant radiotherapy. Local recurrence occurred after more than 10 years, metastases after 15 years.

[Survival rate of a cement-free cup of titanium with laser structured surface]. / Uberlebensrate einer zementfreien Pfanne aus Reintitan mit laserstrukturierter Oberfläche.

PURPOSE: So far no clinical results concerning the survival rates of cementless pure titanium cups with laser-structured surfaces exist. This study was performed to evaluate our results for the Alphasegment acetabular component (Alphanorm). METHOD: Retrospective analysis of 50 cups in 45 patients was performed (operations performed between November 1995 and January 1998). The average age at the time of the implantation was 65.1 years. Dysplastic hips and revisions were excluded. The survival rate was calculated according to the Kaplan-Meier analysis with the end point defined as the revision surgery of the cup. RESULTS: The average follow-up period was 2.9 (0.6-4.0) years. Two patients (i.e., two implants) died during the observation period, none were lost for follow-up. Six of the cups had to be revised due to aseptic loosening. The survival rate at 3.2 years after implantation was 87%. None of the stems had to be revised. CONCLUSIONS: Further use of the cementless hemispherical pure titanium cup with laser-structured surface cannot be recommended. The observed prevalence of loosening for the Alphasegment acetabular components was higher than for other cups. Close follow-up of patients with this type of implant is necessary.

[Complete dislocation of the polyethylene inlay after internal hemipelvectomy and individually fitted tumor endoprosthesis]. / Komplette Luxation des PE-Inlays nach innerer Hemipelvektomie und individueller Tumorendoprothese.

We report about an exceptional complication after internal hemipelvectomy and replacement of the defect with a custom-made endoprosthesis. A complete luxation of the PE-inlay out of the metal cup occurred. Radiologically we assumed a luxation of the femoral head in dorsal direction. Revision after a failed attempt of closed reposition showed a complete luxation of the inlay, which was caused by deficient fixation in the acetabular component. The absence of a contrast wire in the PE-inlay delayed the right diagnosis and made it difficult to find the dislocated inlay in the large wound.

[Early loosening of a cemented hip endoprosthesis stem of titanium]. / Frühlockerungen eines zementierten Hüftendoprothesenstiels aus Titan.

Up to now there are no facts concerning the loosening rate of the cemented titanium stem (Trios). The central guiding canula and the longitudinal drilled stem shall ensure a symmetric cement mantle. In order to estimate the risk of aseptic loosening all Trios prostheses implanted in our clinic (n = 67; operations 1/95-11/96; max. follow-up: 3.1 years) were examined in a retrospective study and compared with a conventional femoral component (n = 141; Müller special; CoCr; operations 1977-1982). We used survivorship analysis to assess the results (Kaplan-Meier method; end point: revision). Compared to the conventional femoral stem the survival rate of the Trios prostheses was significantly worse (p = 0.0001). The probability of no revision after 3 years was 72% (conventional femoral component: 96%). Preoperative x-rays showed radiolucent lines surrounding the cement mantle. These findings as well as the loosening at the cement metal interface were confirmed intraoperatively. The explanted stems showed corresponding signs of abrasion on the surface. Our results prove that the application of cemented titanium stems might be problematic. With regard to the Trios prosthesis we recommend close routine check-ups to keep the chance of an early revision.

Improvement of the cement mantle of the acetabular component with bone cement spacers. A retrospective analysis of 200 cemented cups.

A discontinuous or thin cement mantle of a socket is associated with increased polyethylene wear and cement fractures. In a retrospective radiological analysis we examined the quality of the cement mantle in cups without (group I = 100 Charnley-Mueller cups) and with (group II = 100 Contemporary cups, Howmedica) bone cement spacers. Under-filling (0-2 mm) and over-filling (> 8 mm) of the cement mantle were noted and classified. Statistics show significantly less under-filling of the cement mantle in group II than in group I (P = 0.001), in particular when comparing separate cup regions (thirds: P << 0.001). Furthermore, there is no significant difference in the frequency of overfilling with cement between groups I and II (P = 0.108). To sum up, utilization of an acetabular component with performed bone cement spacers considerably improves the quality of the cement mantle without additional cost.